Additional file 2 – Calculating 10-year risk estimates for fatal CVD [35]
Step 1
Calculate the underlying risks for coronary heart disease and for non-coronary
cardiovascular disease separately for the person's age now (for this study, age now is
set as 60) and for their age in ten years time, using the values for alpha and p shown in
Table 1. The underlying survival probability, S0, is given by:
S0(60) = exp{–(exp(α))(60 – 20)p}
S0(70) = exp{–(exp(α))(60 – 10)p}
Step 2
Using the coefficients in Table 2, calculate the weighted sum, w, of the risk factors
cholesterol, smoking and systolic blood pressure. Two weighted sums will have to be
calculated, one for coronary heart disease and one for non-coronary cardiovascular
disease. Smoking is coded as 1 for current and 0 for non-smoker, so no value for
smoking has to be entered if the person is a non-smoker. Cholesterol is measured in
mmol/L and SBP is measured in mmHg. The weighting for each risk factor is denoted
by beta.
w =βchol(cholesterol – 6) + βSBP(SBP – 120) + βsmoker(current)
Step 3
Combine the underlying risks for coronary heart disease and for non-coronary
cardiovascular disease, at the person's age and at their age ten years from now (four
calculations) which were calculated in step 1 with the weighted sum of a person's risk
factors from step 2 for the two end-points, coronary heart disease and non-coronary
cardiovascular disease to get the probability of survival at each age for each cause.
S(60) = {S0(60}exp(w)
S(70) = {S0(70)}exp(w)
Step 4
For each cause, calculate the 10-year survival probability based on the survival
probability for the person's current age and their age in 10 years time:
S10(60) = S(70) /S(60)
Step 5
Calculate the 10 year risk for each end-point as
Risk10 = 1 - S10(60)
Step 6
Combine the risks for coronary heart disease and non-coronary cardiovascular disease
by adding them:
CVDRisk10(60) = [CHDRisk(60)] + [Non-CHDRisk(60)]